Is highly a noun

No, the Word 'highly' is the adverb form of the adjective 'high'.

The noun form of the adjective 'high' is highness.

The Word 'high' is also a noun form as a Word for a lofty place; a period or situation in which something reaches its highest level; a setting on a transmission, oven, or other device; an atmospheric condition; a feeling of great happiness or excitement; an informal (slang) Word for an intoxicated condition induced by alcohol or drugs; a Word for a thing.